Typically the UV stage will be last because you want the water to be free from any microscopic particles and contaminants. Bacteria and cysts can be shaded behind particles when passing through the UV stage.

Pre and Post carbon filters are also common with UV systems. If your pre-filters reduce down to 0.5 microns or less, you should be able to use the Carbon VOC filter after the UV light.

PVC can be used, but you do not want it to come in contact with direct UV light. Typical PVC exposed to UV will cause yellow discoloration and cause it to become brittle after long exposure. You shouldn't have any issue as long as the light doesn't shine on the PVC.

Using PVC upstream or downstream will have no-effect from water that was treated with UV light.

It will depend on the turbidity of the water. If color or suspended particles are present (cloudiness), the penetrating quality of the UV light is reduced and contamination is able to pass through. If you notice this issue, a carbon filter would be needed after the sediment and before the UV light.

How many Gallons per minute were you needing to process? Do you have a UV light that will be able to effectively handle your demand?

Our original water supply was coming from the Marina where we are at but have just recently been informed that we are going to have to supply our own water which will need to be pulled from the lake. We have never drank the water there anyway but we do use it for washing dishes and showers.

The cabins backup water pump is about 8 GPM from my estimation, I was going to install a larger UV more like a 12 GPM unit just to make sure. I have not had a opportunity to have the water tested as of yet because it is closed up and winterized for the season, but we will need to have something in the works that we can use at the start of the new season.
With that being the case,I should plan on putting the Carbon VOC before the UV light to start out with?

If you were looking for atleast 12 GPM unit, the Polaris UV-12C will accommodate disinfecting the water effectively.

Also, you may see more turbid water after storms or higher/lower water levels. Keep in mind that you do not want to pull water too close to the surface or the bottom.

A pre and post carbon block filter may be necessary for different water conditions. The Pentek 150469 with the KX Matrikx 02-425-125-975 should accommodate the flow rates needed after the sediment prefilters.